NAD+ delivery methods: what the evidence says vs. what TikTok claims

What did @kristinastout actually say?

Kristina, a nurse practitioner, ranked three NAD+ delivery routes from best to worst: IV infusion first, subcutaneous injections second, and oral supplements last. Her reasoning was straightforward: absorption drives the ranking. She called IV "by far the best way to get NAD" because it goes directly into the bloodstream, said injections still beat oral options, and was blunt about oral supplements, noting they take a long time to build up and she personally doesn't recommend them because she hasn't tried them herself. She also mentioned she personally uses injections and sees benefits within a couple of days. The pitch at the end, inviting viewers in her licensed states to become her patients, is worth noting as context for the recommendations.

This is a fairly restrained, commercially honest breakdown by medspa standards. She didn't claim NAD+ cures anything specific, and she flagged cost differences. But there are several places where the science deserves a harder look.

Does the science back this up?

The absorption hierarchy she describes is directionally correct, but "by far" is doing a lot of heavy lifting throughout this video. The research on NAD+ bioavailability across delivery routes is still maturing, and the clinical evidence for any route producing reliable, measurable benefits in healthy people is thinner than the medspa industry suggests.

IV NAD+ does achieve 100% bioavailability by definition since it bypasses the gut entirely. That part is not controversial. Subcutaneous injections of NAD+ precursors or NAD+ itself do show meaningful absorption, though direct comparisons with IV are not well-documented in peer-reviewed literature for this specific molecule. The more studied route involves oral precursors, particularly NMN (nicotinamide mononucleotide) and NR (nicotinamide riboside), not NAD+ itself. Research by Trammell et al. (2016, Nature Communications) confirmed oral NR raises blood NAD+ levels in humans. A 2023 trial by Yoshino et al. (Cell Metabolism) showed oral NMN improved muscle insulin sensitivity in postmenopausal women. So oral precursors are not as ineffective as the framing here implies.

The claim that injection benefits appear "within a couple of days" is anecdotal. No controlled trial has established that timeline for subcutaneous NAD+ injections specifically.

What did they get wrong (or right)?

She got the general absorption hierarchy right, but oversimplified it in ways that matter.

• Right: IV achieves maximal bioavailability. That is basic pharmacokinetics, not a controversial claim.
• Partly wrong: Oral NAD+ supplements are not the same as oral NAD+ precursors. Most commercial products use NR or NMN, which are converted to NAD+ after absorption. Lumping these together as poorly absorbed is misleading. Trammell et al. (2016) showed NR raises whole-blood NAD+ by up to 2.7-fold after a single dose.
• Unverifiable: "You see the benefits with injections pretty quickly within a couple days." This is self-reported experience, not clinical data. There are no randomized trials comparing subcutaneous NAD+ injections to placebo with a two-day outcome measure.
• Reasonable: Her disclosure that she doesn't recommend oral supplements partly because she hasn't tried them is actually more honest than most wellness creators, even if it's an odd clinical rationale.

The bigger issue is that framing three delivery routes as a clear hierarchy implies the clinical benefits of NAD+ supplementation are established across healthy adults. They are not. Most robust evidence comes from older adults or people with specific metabolic conditions.

What should you actually know?

NAD+ declines with age, and there is legitimate scientific interest in whether supplementation matters. But the gap between "this molecule matters biologically" and "paying for IV infusions will make you feel better" is large, and the medspa industry routinely skips over it.

Here is what the current evidence actually supports:

• Oral NR and NMN raise blood NAD+ levels in humans. This is replicated. Whether raised NAD+ levels translate to felt benefits in healthy adults is not yet settled.
• IV NAD+ is used clinically in some addiction medicine contexts, but evidence for its use in general wellness is largely anecdotal and not drawn from controlled trials.
• Subcutaneous NAD+ injections are offered widely in telehealth and medspa settings, but peer-reviewed data on this specific route for this molecule is sparse.
• Cost matters. IV infusions can run several hundred to over a thousand dollars per session. If the clinical evidence for superiority over a well-formulated oral precursor is weak, the cost-benefit calculation changes significantly.

If you are considering any form of NAD+ therapy, ask your provider what specific outcome they are targeting and what evidence supports that outcome at that delivery route. "Absorption" is not the same as "clinical benefit."